Ultrasound- and circumference-based quadriceps mass is an independent predictor of 28-day mortality in critically ill patients

Background Skeletal muscle mass is a key indicator of physiological reserve in critical illness. Objective This study aimed to evaluate whether quadriceps mass assessed by bedside methods predicts 28-day mortality in critically ill patients. Methods In this prospective study of 603 critically ill adults, we measured quadriceps thickness by ultrasonography under minimal transducer pressure (QT-min) and maximal transducer pressure (QT-max), quadriceps circumference (QC), and mid-upper arm circumference (MUAC) at admission. Cox regression was used to analyze the association between quadriceps thickness and 28-day mortality. Interaction and subgroup analyses were conducted for age, sex, BMI, mechanical ventilation, number of organ supports and vasopressor use. Results The 28-day mortality rate was 21.06% (127/603). After adjustment in Model 3, QC (HR 0.95 per 1-cm increase, 95% CI 0.91–1.00), QT-min (HR 0.63 per 1-cm increase, 95% CI 0.42–0.92), and QT-max (HR 0.42 per 1-cm increase, 95% CI 0.20–0.85) remained independent protective factors for mortality, while MUAC do not. Significant interactions were found for QT-min with vasopressor use and organ support ( q < 0.05), with protective effects observed only in patients without these conditions. Conclusion Bedside quadriceps mass assessment independently predicts 28-day mortality in critically ill patients, supporting its use for early risk stratification. In patients requiring vasopressors or organ support, the prognostic value of QT-min was attenuated, suggesting it may be susceptible to illness severity. However, given the small size of these subgroups, this finding warrants a cautious interpretation.